1. Field of the Invention
This invention relates generally to perpendicular magnetic recording systems, and more particularly to perpendicular magnetic recording write heads for use in magnetic recording disk drives.
2. Description of the Related Art
In a perpendicular magnetic recording system like a magnetic recording hard disk drive, the recorded bits are stored in a perpendicular or out-of-plane orientation in the recording layer. The recording or write head in perpendicular magnetic recording disk drives includes a write pole comprising a shaped pole and a main pole for writing to the recording layer, and one or more return poles for return of magnetic flux from the recording layer.
The main pole is typically formed of high moment magnetic materials, the most common example being iron-cobalt (FeCo) alloys. One of the problems with the high-moment main pole is “erase-after-write”, i.e., the undesirable erasure of information after writing. This is due to the high-moment main pole having a high remanent magnetization or remanence, i.e., the magnetization that remains after the magnetic field is removed. It is known that remanence can be reduced by forming the main pole as a lamination of multiple ferromagnetic layers. One common lamination approach is the use of an antiferromagnetically coupling (AFC) film between two FeCo layers. The two antiferromagnetically coupled FeCo layers have antiparallel magnetizations that substantially cancel each other in the absence of a magnetic field, thus resulting in low remanence.
In addition to low remanence, the main pole should also have high magnetic permeability for quick response. Permeability (μ) is defined as the ratio Bs/H95, where Bs is the saturation magnetization and H95 is the magnetic field required for 95% saturation. However, a disadvantage of the laminated main pole with antiferromagnetically coupled FeCo layers is increased saturation field, and thus decreased permeability.
Antiferromagnetically-coupled laminated main poles have been described with a Ru AFC film between two FeCo layers (U.S. Pat. No. 7,057,853), a Ru AFC film between two NiFe layers (U.S. Pat. No. 7,159,302 and U.S. Pat. No. 7,436,629) and a Cr AFC film between two FeCo layers (U.S. Pat. No. 7,656,611 B2). U.S. Pat. No. 7,064,924 describes an antiferromagnetically-coupled laminated main pole with very thin (2-4 Å) NiFe films between a Ru AFC film and the FeCo layers for adjusting the coupling strength across the AFC film.
What is needed is a perpendicular magnetic recording write head that has an improved laminated main pole with both low remanence and high permeability.